Industrial process pressure transmitters are used to measure the pressure of an industrial process fluid such as a slurry, liquid, vapor or gas in chemical, pulp, petroleum, gas, pharmaceutical, food and/or other fluid processing plants. Industrial process fluid pressure transmitters are often placed near the process fluids, or in field applications. Often these field applications are subject to harsh and varying environmental conditions that provide challenges for designers of such transmitters.
The sensing element in many process fluid pressure transmitters is often a capacitance-based sensor that includes a deflectable sensing diaphragm and two or more capacitance electrodes. A dielectric fill-fluid is often used between the capacitance plates and the diaphragm. An isolation diaphragm generally interfaces with the process fluid and prevents the process fluid, which at times can be harsh, corrosive, dirty, contaminated, or at an extremely elevated temperature, from interacting with the components of the sensor. Generally, the process fluid acts against the isolation diaphragm generating a deflection of the isolation diaphragm that moves, or otherwise displaces, the fill-fluid behind the diaphragm, which fill-fluid then accordingly moves or otherwise displaces the sensing diaphragm of the pressure sensor. The pressure sensor has an electrical characteristic, such as capacitance, that varies with the applied pressure and that electrical characteristic is measured, or otherwise determined, by measurement circuitry within the process fluid pressure transmitter and an output signal related to the process fluid pressure is generated. This output signal can further be formatted in accordance with known industry standard communication protocols and transmitted through a process communication loop to other field devices, or a controller.
As the state of the art for process fluid pressure transmitters has advanced, sensing techniques and accuracy have improved. However, manufacturers of such devices are still called upon to provide devices with more exacting precision and accuracy. Accordingly, providing a process fluid pressure transmitter with improved accuracy and precision would benefit the art of industrial process measurement and control.